A common difficulty with portable equipment is the gradual decline in battery performance after the first year of service. Although fully charged, the battery eventually regresses to a point where the available energy is less than half of its original capacity(Toshiba PA3535U-1BRS battery).

Rechargeable batteries are known to cause more concern, grief and frustration than any other component of a portable device. Given its relatively short life span, the battery is also one of the most expensive and least reliable parts. In many ways, a battery exhibits human-like characteristics: it needs good nutrition, prefers moderate room temperature and with the nickel-based system, requires regular exercise to prevent the phenomenon called 'memory'(Toshiba PA3534U-1BRS battery).

How to restore and prolong nickel-based batteries

When nickel-based batteries are mentioned, the word 'memory' comes to mind. Memory was originally derived from 'cyclic memory', meaning that a Nickel-cadmium (NiCd) battery could remember how much energy was required and would provide similar amounts on subsequent discharges. Improvements in battery technology have virtually eliminated this phenomenon. The modern term of 'memory' is a crystalline formation that robs the battery of its capacity. Applying one or several full discharge cycles can commonly reverse this effect (Toshiba PA3399U-2BRS battery).

The active cadmium material of a NiCd battery is present in finely divided crystals. In a good cell, these crystals remain small, obtaining maximum surface area. Memory causes the crystals to grow, reducing the surface area. In advanced stages, the sharp edges of the crystals may penetrate the separator, initiating high self-discharge or an electrical short (Toshiba PA3399U-1BRS battery).

The effect of crystalline formation is most visible if a NiCd battery is left in the charger for days, or if repeatedly recharged without a periodic full discharge. Since most applications do not use up all energy before recharge, a periodic discharge to 1V/cell (known as exercise) is essential to prevent memory (Toshiba PA3285U-1BRS battery).

All NiCd batteries in regular use and on standby mode (sitting in a charger for operational readiness) should be exercised once per month. Between these monthly exercise cycles, no further service is needed and the battery can be used with any desired user pattern without memory concern (Toshiba PA3465U-1BRS battery) .

If no exercise is applied to a NiCd for three months or more, the crystals ingrain themselves, making them more difficult to break up. In such a case, exercise may no longer be effective in restoring a battery and reconditioning is required. Recondition is a secondary discharge that slowly removes the remaining battery energy by draining the cells to virtually zero volts. NiCd batteries can tolerate a small amount of cell reversal. During deep discharge, caution must be applied to stay within the allowable current limit to minimize cell reversal (Toshiba PA3450U-1BRS battery).

When Nickel-Metal Hydride (NiMH) was introduced in the early 1990s, there was much publicity about its memory-free status. Today we know that NiMH also suffers from memory but to a lesser extent than NiCd. No scientific research is available that specifies optimal maintenance. Applying a full discharge once every three months appears right. Because of the shorter service life, over-exercising of NiMH is not recommended (Toshiba PA3285U-1BRS battery ).

Simple Guidelines

1. Do not leave a nickel-based battery in a charger for more than a day with the 'ready' light on. It is better to remove the battery from the charger and applying a charge before use.
2. Apply periodic discharge cycles. Running the battery down in the equipment may do this also.
3. It is not necessary to discharge the battery before each charge. This would put undue stress on the battery (Sony VGN-FZ150E battery).
4.Avoid elevated temperature. The battery should cool off and remain at ambient temperature after full-charge.
5.Use high quality chargers.

The effect of zapping

Remote control (RC) racing enthusiasts have experimented with all imaginable methods to maximize battery performance. One technique that seems to work is zapping the cells with a very high pulse current. Zapping is said to increase the cell voltage by 20 to 40mV under a 30A load. According to experts, the voltage gain is stable; only a small drop is observed with usage and age (IBM ThinkPad R50 battery).

During the race, the motor draws 30A from a 7.2V battery. This calculates to over 200W or close to a quarter HP of power. The race lasts about four minutes.

According to experts, zapping works best with NiCd cells. NiMH cells have been tried but the results are inconclusive. Zapping is done with a 47,000mF capacitor charged to 90V. Best results are achieved if the battery is cycled twice after treatment, then zapped again. Once in service, zapping no longer improves the cell's performance. Neither does zapping regenerate a cell that has become weak (IBM ThinkPad R60 battery).

Companies specializing in zapping batteries use top quality Japanese-made NiCd cells. The cells are normally sub-C and are handpicked at the factory. Specially labeled, the cells arrive in discharged state with open cell voltages of 1.11 to 1.12V. If below 1.06V, the cell is suspect and zapping does not work well (IBM ThinkPad R51 battery).

There are no apparent side effects to zapping but the battery manufacturers remain non-committal. No scientific explanation is available and only little is known on the longevity of the cells after treatment (IBM ThinkPad X41 Tablet battery).

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